applied physics letters

石墨烯异质结构的电子传输虽然氮化硼底物被用来实现电子在石墨烯场效晶体管中高速电子迁移，但是目前尚不清楚其他分层的二维晶体是否比石墨烯的电子性能优越，在这篇文章里面，我们将研究在石墨烯 表 关于同志近三年现实表现材料材料类招标技术评分表图表与交易pdf视力表打印pdf用图表说话 pdf 面的硒化镓和过渡金属(二硫化钨、二硫化钼晶体）对石墨烯电子质量的影响，根据原子力显微镜显示表明，相比传统的二氧化硅基质这些晶体表面粗糙程度很低其方均根值也只有0.1nm，结果表明石墨烯设备具有很高的电子迁移率。除石墨烯以外绝缘的二维新材料，比如硒化镓ws2、mos2、表现出许多奇异电子光学，自旋电子学，和机械属性。最近近期发展在这些超细平面结构上给互相明确地提出了杰出的基础和应用研究的机会，列如用平的石墨烯代替二氧化硅基质显著地增强了石墨烯的电子流动，以便观察在室温下的弹道运输和少部分的量子霍尔效应。将石墨烯和氮化硼，ws2等结合成异质结构被证明能制成高能灵敏的光伏设备。在这篇文章中，我们研究各种各样的基质中石墨烯的电子质量，而ws2和wos2也表现出类似的化学和结构性能，在电子迁移率中G-ws异质结构显示出是4倍的G-wos导体性能，使得在选择其中一个的时候，ws2比较有吸引力，我们观察到在饱和导电性能也高于阀值电压。硒化镓在我们的环境中比较少量，在石墨烯设备制造上，硒化镓晶体表现出更低的电子迁移性。在相比二氧化硅基质中，结果表明石墨烯为最佳理想选择。去研究晶体的表面形态，微机械剥离法用来储存相对来说要厚的晶体氮化硼、ws2、mos2、硒化镓的结构调查，用暗场成像技术实现选择潜在的候选材料其表面-300um的清洁面积和高度-20nm，图像一中表明，在经过热处理过后，通过原子力显微镜中看出氮化硼、ws2、和mos2发裂，我们注意到与其他晶体相比，在周围环境下，如果在热处理之后，硒化镓晶体腐蚀更快或者保持高强度的光强，在没有经过热处理中，如图片1d和1e所示，硒化镓的AFM图片中，在表皮剥落后一天，将发裂。Electronictransportingraphene-basedheterostructures ABSTRACTWhileboronnitride (BN) substrateshavebeenutilizedtoachievehighelectronic mobilities ingraphene fieldeffecttransistors,itisunclearhowotherlayeredtwodimensional(2D)crystalsinfluencetheelectronicperformanceof graphene. InthisLetter,westudythe surfacemorphology of2D BN, galliumselenide(GaSe),andtransitionmetaldichalcogenides(tungstendisulfide(WS2)andmolybdenumdisulfide(MoS2))crystalsandtheirinfluenceongraphene's electronicquality.Atomicforcemicroscopyanalysisshowsthatthesecrystalshaveimprovedsurfaceroughness(rootmeansquarevalueofonly∼0.1 nm)comparedtoconventionalSiO2 substrate.Whileourresultsconfirmthat graphene devicesexhibitveryhighelectronic mobility (μ)on BN substrates, graphene devicesonWS2 substrates(G/WS2)areequallypromisingforhighqualityelectronictransport(μ ∼ 38 000cm2/Vsatroomtemperature),followedbyG/MoS2 (μ ∼ 10 000cm2/Vs)andG/GaSe(μ ∼ 2200cm2/Vs).However,weobserveasignificantasymmetryinelectronandholeconductioninG/WS2 andG/MoS2 heterostructures, mostlikelyduetothepresenceofsulphurvacanciesinthesubstratecrystals.GaSecrystalsareobservedtodegradeovertimeevenunderambientconditions,leadingtoalarge hysteresis in graphene transportmakingitalesssuitablesubstrate.Isolatednewtwodimensional(2D)materialsbeyondgraphene,suchasWS 2,MoS 2,andGaSe,exhibitmanyexoticelectronic, 1optical, 2–4 spintronics, 5 andmechanical 6 properties.Recentdevelopmentinthetransferoftheseultrathinplanarstructuresontoeachotherwithprecisecontroloffersoutstandingopportunitiesforfundamentalandappliedstudies.Forexample,thereplacementofcommonsilicondioxide(SiO 2)substratewithultraflatboronnitride(BN)crystalresultedinasignificantenhancementinelectronicmobilityofgraphenethatallowedtheobservationofroomtemperature(RT)ballistictransport, 7,8 andfractionalquantumHalleffect. 9 CombinationofgraphenewithBN,WS 2,andMoS 2 crystalsalsoenablednewmemoryandtransistorconcepts. 10,11 Recently,grapheneandWS 2-basedheterostructureshavebeendemonstratedinhighlyflexiblephotovoltaicdeviceswithextremelyhighexternalquantumefficiency. 12 GraphenebasedheterostructuredevicesbuiltwithMoS 2orGaSearealsoexpectedtoexhibitsimilarbehavior.Lastbutnotleastimportant,WS 2 wasproposedtoenhancetheweakspinorbitcouplingofgraphenewithaproximityeffect. 13 Sincegrapheneandthese2Dcrystalsarethemostactiveelementsincurrentandpossiblyfutureheterostructuredevices,itisimportanttounderstandtheimpactofthesecrystalsontheelectronicqualityofgraphenebeforebuildingincreasinglycomplexheterostructures.InthisLetter,westudytheelectronicqualityofgrapheneonvarioussubstrates.WhileWS 2 andMoS 2 havesimilarchemicalandstructuralproperties,G/WS 2 heterostructuresexhibitfour-foldhigherelectronicmobilitythanthatofG/MoS 2,makingWS 2 anattractivealternativetoBNsubstrates.WeobserveconductivitysaturationonelectronsideaboveathresholdvoltageinG/WS 2devices.GaSecrystalsarefoundtobelessinerttoambientconditions,andgraphenedevicesfabricatedonGaSecrystalsexhibitevenlowermobilitiesthanthegraphenedevicesonSiO 2 substrates.Ourresultsdemonstratetheimportanceofidealchoiceofmaterialforgraphene-basedheterostructuredevices.Tostudythesurfacemorphologyofcrystals,micromechanicalexfoliationmethodisemployedtodepositrelativelythickcrystalsofBN, 14 WS 2, 15 MoS 2 (StructureProbeInc.-SPI,naturalmolybdenite),andGaSe(HQGraphene)onSi/SiO 2 wafers.Darkfieldimagingtechniqueisimplementedtoselectthepotentialcandidateflakesofa ∼ 300  μm 2 cleansurfaceareaandaheightof∼20 nm.Figs. 1(a)–1(c) showthetypicalAFMimagesofBN,WS 2,andMoS 2 flakesafterannealinginAr/H 2 (9/1)gaseousmixtureat400 °Cfor6htoremovepossibletaperesidues.Wenoticedthatunlikeothercrystals,GaSecrystalscorrodeevenunderambientconditionsandcorrodefasteriftheflakesareannealedorkeptunderstrongintensityoflight.TheAFMimagesofGaSeflakesimmediatelyafterexfoliationand1dayafterexfoliationwithoutannealingareshowninFigs. 1(d)and1(e) ,respectively.TheheighthistogramsofthecrystalsareshowninFig. 1(g) andcorrespondingrmsroughnessofcorrespondingcrystalsaresummarizedinFig. 1(h) .Fig. 1(f) istheAFMimageofaconventionalSiO 2 substrateforcomparisonpurpose.BNhastheflattestsurface(∼0.06 nm)followedbyWS 2 (∼0.08 nm),MoS 2 (∼0.09 nm),freshGaSe(∼0.12 nm),andSiO 2 (∼0.17 nm).TheroughnessofaGaSecrystalincreasesfrom0.12 nmto0.185 nmafteronlyonedayeventhoughthesamplewaskeptinhighvacuum,becomingrougherthanSiO 2.Sincetheworkfunctionsofthese2Dmaterialsandgraphenearesimilar,thechargeneutralitypoint(CNP)ofgrapheneisexpectedtobelocatedatthecenterofbandgapofthesecrystals,makingthemviablealternativesubstratetoSiO 2 forgraphenefieldeffecttransistors. 16